Do not close connections immediately on close signal, await for remaining responses

examples/basalt.rs

@@ -1,20 +1,20 @@
+use std::io::Write;
 use std::net::SocketAddr;
 use std::sync::Arc;
 use std::time::Duration;
-use std::io::Write;
 
 use log::{debug, info, warn};
 
-use structopt::StructOpt;
 use serde::{Deserialize, Serialize};
+use structopt::StructOpt;
 
 use sodiumoxide::crypto::auth;
 use sodiumoxide::crypto::sign::ed25519;
 
-use netapp::NetApp;
-use netapp::peering::basalt::*;
 use netapp::message::*;
+use netapp::peering::basalt::*;
 use netapp::proto::*;
+use netapp::NetApp;
 
 #[derive(StructOpt, Debug)]
 #[structopt(name = "netapp")]
@@ -52,7 +52,8 @@ async fn main() {
 	env_logger::Builder::new()
 		.parse_env("RUST_LOG")
 		.format(|buf, record| {
-			writeln!(buf,
+			writeln!(
+				buf,
 				"{} {} {} {}",
 				chrono::Local::now().format("%s%.6f"),
 				record.module_path().unwrap_or("_"),
@@ -62,7 +63,6 @@ async fn main() {
 		})
 		.init();
 
-
 	let opt = Opt::from_args();
 
 	let netid = match &opt.network_key {
@@ -108,9 +108,11 @@ async fn main() {
 		|_from: ed25519::PublicKey, msg: ExampleMessage| {
 			debug!("Got example message: {:?}, sending example response", msg);
 			async {
-				ExampleResponse{example_field: false}
+				ExampleResponse {
+					example_field: false,
 				}
 			}
+		},
 	);
 
 	tokio::join!(
@@ -120,8 +122,6 @@ async fn main() {
 	);
 }
 
-
-
 async fn sampling_loop(netapp: Arc<NetApp>, basalt: Arc<Basalt>) {
 	loop {
 		tokio::time::delay_for(Duration::from_secs(10)).await;
@@ -132,9 +132,10 @@ async fn sampling_loop(netapp: Arc<NetApp>, basalt: Arc<Basalt>) {
 
 			let netapp2 = netapp.clone();
 			tokio::spawn(async move {
-				match netapp2.request(&p, ExampleMessage{
+				match netapp2
-					example_field: 42,
+					.request(&p, ExampleMessage { example_field: 42 }, PRIO_NORMAL)
-				}, PRIO_NORMAL).await {
+					.await
+				{
 					Ok(resp) => debug!("Got example response: {:?}", resp),
 					Err(e) => warn!("Error with example request: {}", e),
 				}

examples/fullmesh.rs

@@ -1,5 +1,5 @@
-use std::net::SocketAddr;
 use std::io::Write;
+use std::net::SocketAddr;
 
 use log::info;
 
@@ -32,7 +32,8 @@ async fn main() {
 	env_logger::Builder::new()
 		.parse_env("RUST_LOG")
 		.format(|buf, record| {
-			writeln!(buf,
+			writeln!(
+				buf,
 				"{} {}	{} {}",
 				chrono::Local::now().format("%s%.6f"),
 				record.module_path().unwrap_or("_"),

src/conn.rs

@@ -1,17 +1,18 @@
 use std::collections::HashMap;
 use std::net::SocketAddr;
-use std::sync::atomic::{self, AtomicU16};
+use std::sync::atomic::{self, AtomicBool, AtomicU16};
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 
-use async_trait::async_trait;
 use bytes::Bytes;
-use log::{debug, trace};
+use log::{debug, error, trace};
 
 use sodiumoxide::crypto::sign::ed25519;
 use tokio::io::split;
 use tokio::net::TcpStream;
 use tokio::sync::{mpsc, oneshot, watch};
 
+use async_trait::async_trait;
+
 use kuska_handshake::async_std::{
 	handshake_client, handshake_server, BoxStream, TokioCompatExt, TokioCompatExtRead,
 	TokioCompatExtWrite,
@@ -29,7 +30,7 @@ pub(crate) struct ServerConn {
 
 	netapp: Arc<NetApp>,
 
-	resp_send: mpsc::UnboundedSender<(RequestID, RequestPriority, Vec<u8>)>,
+	resp_send: mpsc::UnboundedSender<Option<(RequestID, RequestPriority, Vec<u8>)>>,
 	close_send: watch::Sender<bool>,
 }
 
@@ -78,9 +79,20 @@ impl ServerConn {
 
 		let conn2 = conn.clone();
 		let conn3 = conn.clone();
+		let close_recv2 = close_recv.clone();
 		tokio::try_join!(
-			conn2.recv_loop(box_stream_read, close_recv.clone()),
+			async move {
-			conn3.send_loop(resp_recv, box_stream_write, close_recv.clone()),
+				tokio::select!(
+					r = conn2.recv_loop(box_stream_read) => r,
+					_ = await_exit(close_recv) => Ok(()),
+				)
+			},
+			async move {
+				tokio::select!(
+					r = conn3.send_loop(resp_recv, box_stream_write) => r,
+					_ = await_exit(close_recv2) => Ok(()),
+				)
+			},
 		)
 		.map(|_| ())
 		.log_err("ServerConn recv_loop/send_loop");
@@ -112,7 +124,7 @@ impl RecvLoop for ServerConn {
 			let net_handler = &handler.net_handler;
 			let resp = net_handler(self.peer_pk.clone(), bytes.slice(5..)).await;
 			self.resp_send
-				.send((id, prio, resp))
+				.send(Some((id, prio, resp)))
 				.log_err("ServerConn recv_handler send resp");
 		}
 	}
@@ -121,11 +133,12 @@ pub(crate) struct ClientConn {
 	pub(crate) remote_addr: SocketAddr,
 	pub(crate) peer_pk: ed25519::PublicKey,
 
-	query_send: mpsc::UnboundedSender<(RequestID, RequestPriority, Vec<u8>)>,
+	query_send: mpsc::UnboundedSender<Option<(RequestID, RequestPriority, Vec<u8>)>>,
+
 	next_query_number: AtomicU16,
-	resp_send: mpsc::UnboundedSender<(RequestID, Vec<u8>)>,
+	inflight: Mutex<HashMap<RequestID, oneshot::Sender<Vec<u8>>>>,
-	resp_notify_send: mpsc::UnboundedSender<(RequestID, oneshot::Sender<Vec<u8>>)>,
+	must_exit: AtomicBool,
-	close_send: watch::Sender<bool>,
+	stop_recv_loop: watch::Sender<bool>,
 }
 
 impl ClientConn {
@@ -163,19 +176,17 @@ impl ClientConn {
 			BoxStream::from_handshake(read, write, handshake, 0x8000).split_read_write();
 
 		let (query_send, query_recv) = mpsc::unbounded_channel();
-		let (resp_send, resp_recv) = mpsc::unbounded_channel();
-		let (resp_notify_send, resp_notify_recv) = mpsc::unbounded_channel();
 
-		let (close_send, close_recv) = watch::channel(false);
+		let (stop_recv_loop, stop_recv_loop_recv) = watch::channel(false);
 
 		let conn = Arc::new(ClientConn {
 			remote_addr,
 			peer_pk: remote_pk.clone(),
 			next_query_number: AtomicU16::from(0u16),
 			query_send,
-			resp_send,
+			inflight: Mutex::new(HashMap::new()),
-			resp_notify_send,
+			must_exit: AtomicBool::new(false),
-			close_send,
+			stop_recv_loop,
 		});
 
 		netapp.connected_as_client(remote_pk.clone(), conn.clone());
@@ -183,11 +194,14 @@ impl ClientConn {
 		tokio::spawn(async move {
 			let conn2 = conn.clone();
 			let conn3 = conn.clone();
-			let conn4 = conn.clone();
 			tokio::try_join!(
-				conn2.send_loop(query_recv, box_stream_write, close_recv.clone()),
+				conn2.send_loop(query_recv, box_stream_write),
-				conn3.recv_loop(box_stream_read, close_recv.clone()),
+				async move {
-				conn4.dispatch_resp(resp_recv, resp_notify_recv, close_recv.clone()),
+					tokio::select!(
+						r = conn3.recv_loop(box_stream_read) => r,
+						_ = await_exit(stop_recv_loop_recv) => Ok(()),
+					)
+				}
 			)
 			.map(|_| ())
 			.log_err("ClientConn send_loop/recv_loop/dispatch_loop");
@@ -199,51 +213,15 @@ impl ClientConn {
 	}
 
 	pub fn close(&self) {
-		self.close_send.broadcast(true).unwrap();
+		self.must_exit.store(true, atomic::Ordering::SeqCst);
+		self.query_send
+			.send(None)
+			.log_err("could not write None in query_send");
+		if self.inflight.lock().unwrap().is_empty() {
+			self.stop_recv_loop
+				.broadcast(true)
+				.log_err("could not write true to stop_recv_loop");
 		}
-
-	async fn dispatch_resp(
-		self: Arc<Self>,
-		mut resp_recv: mpsc::UnboundedReceiver<(RequestID, Vec<u8>)>,
-		mut resp_notify_recv: mpsc::UnboundedReceiver<(RequestID, oneshot::Sender<Vec<u8>>)>,
-		mut must_exit: watch::Receiver<bool>,
-	) -> Result<(), Error> {
-		let mut resps: HashMap<RequestID, Vec<u8>> = HashMap::new();
-		let mut resp_notify: HashMap<RequestID, oneshot::Sender<Vec<u8>>> = HashMap::new();
-		while !*must_exit.borrow() {
-			tokio::select! {
-				resp = resp_recv.recv() => {
-					if let Some((id, resp)) = resp {
-						trace!("dispatch_resp: got resp to {}, {} bytes", id, resp.len());
-						if let Some(ch) = resp_notify.remove(&id) {
-							if ch.send(resp).is_err() {
-								debug!("Could not dispatch reply (channel probably closed, happens if request was canceled)");
-							}
-						} else {
-							resps.insert(id, resp);
-						}
-					}
-				}
-				resp_ch = resp_notify_recv.recv() => {
-					if let Some((id, resp_ch)) = resp_ch {
-						trace!("dispatch_resp: got resp_ch {}", id);
-						if let Some(rs) = resps.remove(&id) {
-							if resp_ch.send(rs).is_err() {
-								debug!("Could not dispatch reply (channel probably closed, happens if request was canceled)");
-							}
-						} else {
-							resp_notify.insert(id, resp_ch);
-						}
-					}
-				}
-				exit = must_exit.recv() => {
-					if exit == Some(true) {
-						break;
-					}
-				}
-			}
-		}
-		Ok(())
 	}
 
 	pub(crate) async fn request<T>(
@@ -262,10 +240,18 @@ impl ClientConn {
 		bytes.extend_from_slice(&rmp_to_vec_all_named(&rq)?[..]);
 
 		let (resp_send, resp_recv) = oneshot::channel();
-		self.resp_notify_send.send((id, resp_send))?;
+		let old = self.inflight.lock().unwrap().insert(id, resp_send);
+		if let Some(old_ch) = old {
+			error!(
+				"Too many inflight requests! RequestID collision. Interrupting previous request."
+			);
+			if old_ch.send(vec![]).is_err() {
+				debug!("Could not send empty response to collisionned request, probably because request was interrupted. Dropping response.");
+			}
+		}
 
 		trace!("request: query_send {}, {} bytes", id, bytes.len());
-		self.query_send.send((id, prio, bytes))?;
+		self.query_send.send(Some((id, prio, bytes)))?;
 
 		let resp = resp_recv.await?;
 
@@ -279,8 +265,17 @@ impl SendLoop for ClientConn {}
 #[async_trait]
 impl RecvLoop for ClientConn {
 	async fn recv_handler(self: Arc<Self>, id: RequestID, msg: Vec<u8>) {
-		self.resp_send
+		let mut inflight = self.inflight.lock().unwrap();
-			.send((id, msg))
+		if let Some(ch) = inflight.remove(&id) {
-			.log_err("ClientConn::recv_handler");
+			if ch.send(msg).is_err() {
+				debug!("Could not send request response, probably because request was interrupted. Dropping response.");
+			}
+		}
+
+		if inflight.is_empty() && self.must_exit.load(atomic::Ordering::SeqCst) {
+			self.stop_recv_loop
+				.broadcast(true)
+				.log_err("could not write true to stop_recv_loop");
+		}
 	}
 }

src/lib.rs

@@ -18,8 +18,8 @@
 pub mod error;
 pub mod util;
 
-pub mod proto;
 pub mod message;
+pub mod proto;
 
 mod conn;
 

src/netapp.rs

@@ -133,18 +133,22 @@ impl NetApp {
 	/// been successfully established. Do not set this if using a peering strategy,
 	/// as the peering strategy will need to set this itself.
 	pub fn on_connected<F>(&self, handler: F)
-		where F: Fn(ed25519::PublicKey, SocketAddr, bool) + Sized + Send + Sync + 'static
+	where
+		F: Fn(ed25519::PublicKey, SocketAddr, bool) + Sized + Send + Sync + 'static,
 	{
-		self.on_connected_handler.store(Some(Arc::new(Box::new(handler))));
+		self.on_connected_handler
+			.store(Some(Arc::new(Box::new(handler))));
 	}
 
 	/// Set the handler to be called when an existing connection (incoming or outgoing) has
 	/// been closed by either party. Do not set this if using a peering strategy,
 	/// as the peering strategy will need to set this itself.
 	pub fn on_disconnected<F>(&self, handler: F)
-		where F: Fn(ed25519::PublicKey, bool) + Sized + Send + Sync + 'static
+	where
+		F: Fn(ed25519::PublicKey, bool) + Sized + Send + Sync + 'static,
 	{
-		self.on_disconnected_handler.store(Some(Arc::new(Box::new(handler))));
+		self.on_disconnected_handler
+			.store(Some(Arc::new(Box::new(handler))));
 	}
 
 	/// Add a handler for a certain message type. Note that only one handler
@@ -240,11 +244,13 @@ impl NetApp {
 	pub fn disconnect(self: &Arc<Self>, pk: &ed25519::PublicKey) {
 		// If pk is ourself, we're not supposed to have a connection open
 		if *pk != self.pubkey {
-			let conn = self.client_conns.read().unwrap().remove(pk);
+			let conn = self.client_conns.write().unwrap().remove(pk);
 			if let Some(c) = conn {
-				debug!("Closing connection to {} ({})",
+				debug!(
+					"Closing connection to {} ({})",
 					hex::encode(c.peer_pk),
-					   c.remote_addr);
+					c.remote_addr
+				);
 				c.close();
 			} else {
 				return;
@@ -268,9 +274,11 @@ impl NetApp {
 	pub fn server_disconnect(self: &Arc<Self>, pk: &ed25519::PublicKey) {
 		let conn = self.server_conns.read().unwrap().get(pk).cloned();
 		if let Some(c) = conn {
-			debug!("Closing incoming connection from {} ({})",
+			debug!(
+				"Closing incoming connection from {} ({})",
 				hex::encode(c.peer_pk),
-				   c.remote_addr);
+				c.remote_addr
+			);
 			c.close();
 		}
 	}

src/peering/basalt.rs

@@ -3,7 +3,7 @@ use std::net::SocketAddr;
 use std::sync::{Arc, RwLock};
 use std::time::Duration;
 
-use log::{trace, debug, info, warn};
+use log::{debug, info, trace, warn};
 use lru::LruCache;
 use rand::{thread_rng, Rng};
 use serde::{Deserialize, Serialize};
@@ -267,15 +267,13 @@ impl Basalt {
 		netapp.on_connected(
 			move |pk: ed25519::PublicKey, addr: SocketAddr, is_incoming: bool| {
 				basalt2.on_connected(pk, addr, is_incoming);
-			}
+			},
 		);
 
 		let basalt2 = basalt.clone();
-		netapp.on_disconnected(
+		netapp.on_disconnected(move |pk: ed25519::PublicKey, is_incoming: bool| {
-			move |pk: ed25519::PublicKey, is_incoming: bool| {
 			basalt2.on_disconnected(pk, is_incoming);
-			},
+		});
-		);
 
 		let basalt2 = basalt.clone();
 		netapp.add_msg_handler::<PullMessage, _, _>(

src/peering/fullmesh.rs

@@ -185,12 +185,10 @@ impl FullMeshPeeringStrategy {
 		);
 
 		let strat2 = strat.clone();
-		netapp.on_disconnected(
+		netapp.on_disconnected(move |pk: ed25519::PublicKey, is_incoming: bool| {
-			move |pk: ed25519::PublicKey, is_incoming: bool| {
 			let strat2 = strat2.clone();
 			tokio::spawn(strat2.on_disconnected(pk, is_incoming));
-			},
+		});
-		);
 
 		strat
 	}

src/proto.rs

@@ -3,14 +3,14 @@ use std::sync::Arc;
 
 use log::trace;
 
-use async_trait::async_trait;
-
 use async_std::io::prelude::WriteExt;
 use async_std::io::ReadExt;
 
 use tokio::io::{ReadHalf, WriteHalf};
 use tokio::net::TcpStream;
-use tokio::sync::{mpsc, watch};
+use tokio::sync::mpsc;
+
+use async_trait::async_trait;
 
 use crate::error::*;
 
@@ -85,19 +85,23 @@ impl SendQueue {
 			}
 		}
 	}
+	fn is_empty(&self) -> bool {
+		self.items.iter().all(|(_k, v)| v.is_empty())
+	}
 }
 
 #[async_trait]
 pub(crate) trait SendLoop: Sync {
 	async fn send_loop(
 		self: Arc<Self>,
-		mut msg_recv: mpsc::UnboundedReceiver<(RequestID, RequestPriority, Vec<u8>)>,
+		mut msg_recv: mpsc::UnboundedReceiver<Option<(RequestID, RequestPriority, Vec<u8>)>>,
 		mut write: BoxStreamWrite<TokioCompat<WriteHalf<TcpStream>>>,
-		mut must_exit: watch::Receiver<bool>,
 	) -> Result<(), Error> {
 		let mut sending = SendQueue::new();
-		while !*must_exit.borrow() {
+		let mut should_exit = false;
-			if let Ok((id, prio, data)) = msg_recv.try_recv() {
+		while !should_exit || !sending.is_empty() {
+			if let Ok(sth) = msg_recv.try_recv() {
+				if let Some((id, prio, data)) = sth {
 					trace!("send_loop: got {}, {} bytes", id, data.len());
 					sending.push(SendQueueItem {
 						id,
@@ -105,6 +109,9 @@ pub(crate) trait SendLoop: Sync {
 						data,
 						cursor: 0,
 					});
+				} else {
+					should_exit = true;
+				}
 			} else if let Some(mut item) = sending.pop() {
 				trace!(
 					"send_loop: sending bytes for {} ({} bytes, {} already sent)",
@@ -113,33 +120,14 @@ pub(crate) trait SendLoop: Sync {
 					item.cursor
 				);
 				let header_id = u16::to_be_bytes(item.id);
-				if write_all_or_exit(&header_id[..], &mut write, &mut must_exit)
+				write.write_all(&header_id[..]).await?;
-					.await?
-					.is_none()
-				{
-					break;
-				}
 
 				if item.data.len() - item.cursor > MAX_CHUNK_SIZE {
 					let header_size = u16::to_be_bytes(MAX_CHUNK_SIZE as u16 | 0x8000);
-					if write_all_or_exit(&header_size[..], &mut write, &mut must_exit)
+					write.write_all(&header_size[..]).await?;
-						.await?
-						.is_none()
-					{
-						break;
-					}
 
 					let new_cursor = item.cursor + MAX_CHUNK_SIZE as usize;
-					if write_all_or_exit(
+					write.write_all(&item.data[item.cursor..new_cursor]).await?;
-						&item.data[item.cursor..new_cursor],
-						&mut write,
-						&mut must_exit,
-					)
-					.await?
-					.is_none()
-					{
-						break;
-					}
 					item.cursor = new_cursor;
 
 					sending.push(item);
@@ -147,26 +135,17 @@ pub(crate) trait SendLoop: Sync {
 					let send_len = (item.data.len() - item.cursor) as u16;
 
 					let header_size = u16::to_be_bytes(send_len);
-					if write_all_or_exit(&header_size[..], &mut write, &mut must_exit)
+					write.write_all(&header_size[..]).await?;
-						.await?
-						.is_none()
-					{
-						break;
-					}
 
-					if write_all_or_exit(&item.data[item.cursor..], &mut write, &mut must_exit)
+					write.write_all(&item.data[item.cursor..]).await?;
-						.await?
-						.is_none()
-					{
-						break;
-					}
 				}
 				write.flush().await.log_err("Could not flush in send_loop");
 			} else {
-				let (id, prio, data) = msg_recv
+				let sth = msg_recv
 					.recv()
 					.await
 					.ok_or(Error::Message("Connection closed.".into()))?;
+				if let Some((id, prio, data)) = sth {
 					trace!("send_loop: got {}, {} bytes", id, data.len());
 					sending.push(SendQueueItem {
 						id,
@@ -174,6 +153,9 @@ pub(crate) trait SendLoop: Sync {
 						data,
 						cursor: 0,
 					});
+				} else {
+					should_exit = true;
+				}
 			}
 		}
 		Ok(())
@@ -182,33 +164,23 @@ pub(crate) trait SendLoop: Sync {
 
 #[async_trait]
 pub(crate) trait RecvLoop: Sync + 'static {
+	// Returns true if we should stop receiving after this
 	async fn recv_handler(self: Arc<Self>, id: RequestID, msg: Vec<u8>);
 
 	async fn recv_loop(
 		self: Arc<Self>,
 		mut read: BoxStreamRead<TokioCompat<ReadHalf<TcpStream>>>,
-		mut must_exit: watch::Receiver<bool>,
 	) -> Result<(), Error> {
 		let mut receiving = HashMap::new();
-		while !*must_exit.borrow() {
+		loop {
 			trace!("recv_loop: reading packet");
 			let mut header_id = [0u8; 2];
-			if read_exact_or_exit(&mut header_id[..], &mut read, &mut must_exit)
+			read.read_exact(&mut header_id[..]).await?;
-				.await?
-				.is_none()
-			{
-				break;
-			}
 			let id = RequestID::from_be_bytes(header_id);
 			trace!("recv_loop: got header id: {:04x}", id);
 
 			let mut header_size = [0u8; 2];
-			if read_exact_or_exit(&mut header_size[..], &mut read, &mut must_exit)
+			read.read_exact(&mut header_size[..]).await?;
-				.await?
-				.is_none()
-			{
-				break;
-			}
 			let size = RequestID::from_be_bytes(header_size);
 			trace!("recv_loop: got header size: {:04x}", id);
 
@@ -216,12 +188,7 @@ pub(crate) trait RecvLoop: Sync + 'static {
 			let size = size & !0x8000;
 
 			let mut next_slice = vec![0; size as usize];
-			if read_exact_or_exit(&mut next_slice[..], &mut read, &mut must_exit)
+			read.read_exact(&mut next_slice[..]).await?;
-				.await?
-				.is_none()
-			{
-				break;
-			}
 			trace!("recv_loop: read {} bytes", size);
 
 			let mut msg_bytes = receiving.remove(&id).unwrap_or(vec![]);
@@ -233,36 +200,5 @@ pub(crate) trait RecvLoop: Sync + 'static {
 				tokio::spawn(self.clone().recv_handler(id, msg_bytes));
 			}
 		}
-		Ok(())
-	}
-}
-
-async fn read_exact_or_exit(
-	buf: &mut [u8],
-	read: &mut BoxStreamRead<TokioCompat<ReadHalf<TcpStream>>>,
-	must_exit: &mut watch::Receiver<bool>,
-) -> Result<Option<()>, Error> {
-	tokio::select!(
-		res = read.read_exact(buf) => Ok(Some(res?)),
-		_ = await_exit(must_exit) => Ok(None),
-	)
-}
-
-async fn write_all_or_exit(
-	buf: &[u8],
-	write: &mut BoxStreamWrite<TokioCompat<WriteHalf<TcpStream>>>,
-	must_exit: &mut watch::Receiver<bool>,
-) -> Result<Option<()>, Error> {
-	tokio::select!(
-		res = write.write_all(buf) => Ok(Some(res?)),
-		_ = await_exit(must_exit) => Ok(None),
-	)
-}
-
-async fn await_exit(must_exit: &mut watch::Receiver<bool>) {
-	loop {
-		if must_exit.recv().await == Some(true) {
-			return;
-		}
 	}
 }

src/util.rs

@@ -1,5 +1,7 @@
 use serde::Serialize;
 
+use tokio::sync::watch;
+
 /// Utility function: encodes any serializable value in MessagePack binary format
 /// using the RMP library.
 ///
@@ -16,3 +18,21 @@ where
 	val.serialize(&mut se)?;
 	Ok(wr)
 }
+
+/// This async function returns only when a true signal was received
+/// from a watcher that tells us when to exit.
+/// Usefull in a select statement to interrupt another
+/// future:
+/// ```
+/// select!(
+///     _ = a_long_task() => Success,
+///     _ = await_exit(must_exit) => Interrupted,
+/// )
+/// ```
+pub async fn await_exit(mut must_exit: watch::Receiver<bool>) {
+	loop {
+		if must_exit.recv().await == Some(true) {
+			return;
+		}
+	}
+}